Magnetic susceptibility measurements are not routinely performed in the petroleum industry either in core analysis laboratories or downhole in wireline logging or measurements while drilling (MWD) operations. Permeability measurements are usually made directly on core samples. This direct measurement requires that the samples be cleaned and measured, which can take several days or weeks for all the core plugs from just one well. Since cutting and processing the core is very expensive, permeability measurements are generally only done on a fraction of the wells drilled. Whilst some techniques, such as nuclear magnetic resonance (NMR), have been used to predict permeability, these are relatively complicated and costly.